Biomedical Engineering Reference
In-Depth Information
8000
7000
6000
5000
4000
3000
2000
1000
0
0
2000 4000 6000 8000 10,000 12,000 14,000 16,000
Z
re
(Ohm)
FIGURE 4.23
Nyquist plot of DNA PANI/PAA-modified BDD before and after hybridization. (From Gu et al.,
J. Phys. Chem. B
,
109, 13611-13618, 2005. With permission.)
F9512) and antihuman IgM (m-chain specific, Sigma F5384). The Nyquist plot after cova-
lent linking of antigen to surfaces is shown in Figure 4.24.
Figure 4.24 shows Nyquist plots of
Z
→
and
Z
→
from 100 to 1.1 MHz, with 10-mV root-mean-
square (rms) modulation for different kinds of antibody-antigen-modified diamond sur-
faces. After anti-IgG and anti-IgM modified, the Cole-Cole plot has only slightly changes in
real component response (
Z
→
changes from 110 to 112
Ω
at 200 kHz). Then the impedance
Z
→
(before and after exposure to anti-IgG) increased from 110 to 190
Ω
at 200 kHz. The author
also gave the electrochemistry equivalent circuit, which is shown in Figure 4.25.
To analyze the principle, an electrochemistry equivalent circuit model with discrete
element has been established, as shown on Figure 4.25. The author separated the interface
into three layers: (1) the space-charge layer of the semiconductors, (2) the tightly packed
organic modification layers, and (3) the more diffuse ionic region and the biomolecular
layer. In this model,
R
sc
and
C
sc
represented the space charge layer of the semiconduct-
ing substrates.
R
dl
and a CPE reflected the densely packed initial functionalization layer
6
5
4
1 MHz
3
2
1 MHz
Starting surface
Exposed to anti-IgM
Exposed to anti-IgG
1
0
0
1
2
3
4
5
6
7
8
9
10
Y'
, 10
-3
(Ω
-1
)
FIGURE 4.24
Nyquist plot measured on a diamond sample modified with IgG and exposed to anti-IgM and anti-IgG (From
Yang, W.,
Analyst
, 132, 296, 2007. With permission.) [143].
